Rain Gardens: A Beautiful, Natural Way to Manage Stormwater Runoff

By Laura Hromadka

Rain Gardens -the very phrase evokes images of lush serenity and fragrant foliage. But what exactly IS a rain garden?

A rain garden is an easy and better way to handle storm runoff. Ever notice how the rainwater landing upon layers of leaves simply disappears, but rain falling upon hard surfaces just collects? Roofs, sidewalks, parking lots, streets and other “gray” infrastructure funnel this runoff furiously into storm drains, swirling with oils, fertilizers, pet waste, grease and trash. It doesn’t have to be this way!

Fortunately, there is a small revolution quietly gaining momentum. From Los Angeles to New York City, municipalities and the people they serve are learning to re-direct roof downspouts and retain the heretofore wasted rain and snow runoff onto natural, well-drained landscaping sites and into rain barrels. The combination of a small swale or depressed area, some simple planning, and gravel, potting soil and vegetation, produces on-site retention of rainfall, chemicals, and sediment that never looked more beautiful. Cities and towns are making use of low impact design (LID) for parking lot planters, rain barrels, grass swaths along sidewalks, permeable pavers, and water-loving plants to disconnect downspouts and store water temporarily where it falls.

Rain gardens (or bio-retention cells! ) are considered a suitable management practice to manage and treat small volumes of stormwater by the New York State Stormwater Management Design Manual. They are considered an "exfilter" or passive filter, allowing bio-retention and combining physical filtering and adsorption with bio-geochemical processes to remove pollutants. They can be integrated into a site easily and work well in combination with other structural management systems.

Concerned about mosquitoes? No need; rain gardens are designed to drain within 24 hours, far less than the 7-12 days needed to lay and hatch a crop of mosquitoes. In fact, many rain gutters provide a better breeding ground than a well-planned rain garden, without the added benefit of attracting bug-loving dragon-flies as flora can do.

For situations without enough space for a full-sized garden, consider a mini-rain garden in a planter. Use the plants and soil to absorb rainwater from your downspout. Even if you're unable to place the planter on soil or a lawn, it will still do some good.


Building a rain garden doesn't need to be difficult. They can be sized and shaped to fit your yard and landscaped with plants that fit the surroundings. The 4 steps are simple:

  1. locate and size
  2. design and build
  3. plant
  4. maintain

There are many how-to manuals available online, including the excellent handbook found thru the Washington State University Extension (http://mason.wsu.edu/WaterQual/documents/Raingarden_handbook.pdf .

Another great manual is the "Rain Garden Manual for Homeowners," produced by the Geauga Soil and Water Conservation District, Northeast Ohio (http://geaugaswcd.com/yahoo_site_admin/assets/docs/2008_Rain_Garden_Manual_POV_lowres.140104842.pdf).

The University of Wisconsin Extension: Madison, WI has posted a useful how-to manual at (http://learningstore.uwex.edu/Rain-Gardens-A-How-to-Manual-for-Homeowners-P372C82.aspx).

Section 9.5.1 of the New York State Stormwater Management Design Manual contains the applicable regulations and instructive recommendations for sizing and design and a suggested plant list http://www.dec.ny.gov/docs/water_pdf/swdmredevelop.pdf and http://www.dec.ny.gov/chemical/29072.html Chapter 9, page 10.

A thorough group of links to all aspects of low impact design projects can be found at http://www.lid-stormwater.net/site_map.htm#Bioretention.

The Hudson Valley has made great in-roads into low-impact runoff design. Visit local examples at:

·  Beacon Institute (multiple projects)

·  Vassar College (rain garden for maintenance building)

·  Culinary Institute of America (Green roof)

·  Dutchess County Community College(bioretention)

·  Benedict Farm stream buffer

·  Walden Bio-retention project

·  Garrison Institute permeable paving

Enhance the beauty of your landscaping, reduce your contribution to public stormwater, and provide storage and cleanup for our beautiful Hudson Valley watershed -- add a rain garden to your landscape this season!